Thermostat



Novas, 1957 w A, RAY m 2,813,426

THERMOSTAT Y Original Filed Jun@ 28. 1950 Snventors WILL/AMv A. RAY W/Lafm' @Bue-scum United States Patent() THERMOSTAT William A. Ray, North HollyWDOd, and. Wilbert C.

Buescher, Alhambra, Calif., assignors to General Controls Co., Glendale, Calif., a corporation of California Original application June 28, 1950, Serial No. 170,756, now Patent No. 2,683,789, dated July 13, 1954. Di- Xgeglnd this application June 17, 1954, Serial No.

3 Claims. (Cl. 7S-363.5)

This invention relates to electrical devices of the circuit controlling type, and more particularly to lbimetallic thermostats. The present application is a division of our copending application Serial No. 170,756 filed June 28, 1950, now Patent No. 2,683,789.

One object of this invention, claimed in said parent application, is to provide means for sealing the contacts of a thermostat or similar control device from dust or other foreign matter. This iS ,0f special importance in connection with a device wherein the interengagement of the contacts occurs gradually, as in a thermostat of the floatingcontact type, as distinguished from one which employs snap-action t-o eiect abrupt closing and opening of the contacts.

Another object of the invention is to minimize the effect of sound waves on a thermostat of the floating-contact type.

As is brought out in the Ray Patent No. 2,274,838 issued March 3, 1942: in a thermostat of the floatingcontact type the contact resistance, even across contacts having clean unoxidized faces, may be a significant factor in the control of an electric circuit whose total resistance is relatively low; the contact resistance upon initial engagement of the contacts being so high that the voltage across the load device (such as a gas valve) is then insufiicient to effect its operation. With gradual increase of contact pressure the contact resistance is reduced until operation of the control device results.

During the period while the contacts are interengaged but their effective resistance is high, rthe thermostat, when it is of the usual bimetallic type, is very sensitive to ordinary sound waves which cause variation of the contact pressure and resistance so that intermittent false operation of the control device may occur. We accomplish the object of minimizing the effect of the sound waves by (l) providing an asymmetric slot in the bimetallic member so as to produce an unharmonious condition therein whereby microphonic action is dampened, or (2) by friction-producing means acting on the free end of the bimetallic member.

For full understanding of the invention, and further appreciation of its objects and advantages, reference is to be had to the following detailed description and accompanying drawing, and to the appended claims.

1n the drawing:

Figure 1 is a side view, mainly in section, of a bimetallic thermostat embodying the invention;

Figure 2 is a perspective view, to slightly reduced scale, of the bimetallic member or strip shown in Fig. l; and

Figure 3 is a side elevation of a modified form of bimetallic thermostat according to the invention.

1n the drawing, the numeral 11 indicates a support for the thermostat, which support may be of any suitable shape and size; the fragmentary portion of .the support shown in the drawing including a hollow cylindrical boss 12 which is externally threaded for a nut 13. Generally indicated by the numeral 14 is a U-shaped bimetallic strip or member, shown per se in Fig. 2, having openings 15 2,813,426 Patented Nov. 1 9, 1,957

and 16 adjacent the ends of its respective side arms 17 and 18. The bimetallic member 14 is mounted by its side arm 17 on the support (opening 15 tting the boss 12) with la spacer 19 between it and the support. Between the side arms of the bimetallic member is a U-shaped arm 20, of resilient metal, having an opening at one of its ends fitting the support-boss 12; the arm 20, as well as the bimetallic member, being clamped to the support by nut 13.

Secured in the opening 16 in arm 18 of the bimetallic member is a shouldered bushing 21 of thermoplastic insulating material; the outer end of the bushing having been headed-over by the application of heat and pressure. Pressed in the ybore of bushing 21 is an electrical contact 22 which cooperates with another contact 23 mounted in an OPQIling through the free end of the resilient arm 20. Secured, as by welding, to arm 20 is a cup-shaped member 24 having a central opening through which the tip of contact 23 protrudes. Covering the open end of cupshaped member 24 is a diaphragm 25, of elastic insulating material such as rubber, having a beaded ange 25 which is snapped-over and tightly grips the flared rim of the cup. The diaphragm 25 yhas a central opening which ts a circumferential recess in bushing 21. A screw 27, threaded in an opening through the support and boss 12, is in engagement with the headed rear end `ot the normally-fixed contact 23 for adjusting the position 0F the same relative to the movable contact 22; the resilient arm 20 being so tlexed that contact 23 is thereby held in engagement with screw 27 in the normal range of adjustrnent of that contact. Between the support and the head of screw 27 is a friction-producing disk spring 2S. For connecting the thermostat in an electric circuit a lead 29 is soldered to the outer end of the movable contact 22; the support 11, to which the normally-fixed contact 23 is electrically connected through arm 20, serving as the other connecting point for the thermostat.

The cup 24 and diaphragm 25 together form a dusttight compartment for the contacts 22 and 23. The diaphragm, because of its elasticity, does not appreciably impede normal movement of the bimetallic member in response to temperature changes. The diaphragm can be readily opened and reclosed, for inspection of the contacts, by stretching its flange 26 out-of and into place on the rim of cup 24.

Referring now more particularly to Fig. 2, the numeral 30 indicates the sides of a slot cut in the bimetallic member 14 and extending from the crook of its U through both side arms of the member to the points indicated in Fig. l by the broken lines 31. The slot 30 extends generally lengthwise of the side arms but asymmetrically with respect to their axes. We have found that by slotting a bimetallic strip obliquely, in the general manner shown, an unharmonious condition is produced in the strip whereby microphonic action of the same under the influence of sound waves is greatly reduced; the disadvantage of such microphonic action, under certain conditions of a thermostat, having been described in the statement of invention.

It is believed that the microphonic-damping effect of the asymmetric slot is produced in the following manner: The point of major ilexure of the U-shaped bimetallic member is at the crook of its U, and at this point the material at one side of the slot is considerably narrower than that at the other side and tends to flex more readily so that a slight twisting or lateral movement of the contact-carrying upper part of arm 18 accompanies any vibration-produced movement of this arm in directions toward and away from the fixed arm 17. This lateral component of movement of arm 18 effects sliding or wiping of one contact on the other which tends to preserve the conductivity of the contacts so that ow of current 3 through them is not appreciably interrupted by the vibrations. indicated by its relative thickness shown) and microphonic vibration of the free arm 18 is therefore so minute that it cannot be appreciated until the contacts are interengaged.

The thermostat shown in Fig. 3 is the same as that of Fig. 1 except for the addition of frictional means for preventing vibration of the bimetallic member. This means comprises a resilient blade 36 secured by a rivet 37 to the horizontal arm of a right-angled bracket 35 which is mounted in place of the spacer 19 of Fig. 1. The blade 36 bears against the top edge of arm 18 of the bimetallic member; a screw 38, passing through an opening in the blade and threaded in the bracket, being provided for adjusting the force of the blade. A small amount of friction between blade 36 and the bimetallic arm 18 is etective to prevent microphonic action of the arm without impeding its normal thermostatic movement. In the arrangement of Fig. 3 it is not necessary to slot the bimetal.

The specific embodiments of our invention herein shown and described are susceptible of modilication without departing from the spirit of the invention, and we intend therefore to be limited only by the scope of the appended claims.

We claim as our invention:

1. In a thermostat: a support; an elongated bimetallic strip of U-shape mounted by one of its side arms on said support, said strip being arranged so that the other of its The bimetallic material is relatively stift (as is arms exes in directions toward and away from said one of its arms in response to temperature Variations, and to sound-wave vibrations; a first element mounted on said support; and a second element carried by said other arm and engageable with said first element when that arm eXes in one direction; said strip having a slot extending lengthwise of both of ,its arms but asymmetrically with respect to the axes thereof to provide unequal amounts of strip-material at opposite sides of said axes so that a lat` eral component of movement accompanies tiexure of said other arm and a sliding action is imparted to said eiements while the same are interengaged.

2. A thermostat according to claim 1 wherein said slot extends through the crook of the U-shaped strip and is at an angle to the common axis of said arms.

3. A thermostat according to claim 2 wherein said slot extends from points in said arms at one side of the center of the strip to a point at said crook at the opposite side of said center.

References Cited in the le of this patent UNITED STATES PATENTS 1,612,114 Hall Dec. 2S, 1926 1,612,375 l Hineline Dec. 28, 1926 2,213,080 Bork Aug. 27, 1940 2,272,458 Eaton Feb. 10, 1942 2,299,562 Burch Oct. 20, 1942 2,602,129 Valverde July l, 1952 

